This invention relates to a mechanical seal and more particularly, to a secondary seal arrangement for a bellows type mechanical seal.
Mechanical face seals are used on various types of machines and equipment, such as pumps, compressors, and turbines which have a rotating shaft and a sealing chamber adjacent the shaft wherein the mechanical seal prevents leakage of fluid from the sealing chamber. Many such mechanical seals include a pair of adjacent seal rings which have opposing seal faces that define a sealing region therebetween to sealingly separate the sealing chamber from an exterior region. Typically, one of the seal rings is mounted on the shaft so as to rotate therewith while the other stationary seal ring is non-rotatably mounted on a seal housing.
Also, at least one of the rotating and stationary seal rings is axially movable. To maintain a seal between the opposed seal faces, the axially movable seal ring is axially loaded, such as by a spring or bellows, towards the other seal ring.
While the sealing region between the relatively rotatable seal faces defines the primary seal, secondary seals are provided between other adjacent components in the mechanical seal. For example, a secondary seal between the rotatable seal ring and the shaft or a shaft sleeve prevents migration of the sealed fluid therebetween, while a secondary seal between the stationary seal ring and a support element therefor prevents migration of the sealed fluid between these components.
More particularly as to a bellows type mechanical seal, a bellows is provided that typically has a bellows adapter at one end which connects to the seal housing and a bellows flange at the opposite end which supports the stationary seal ring. The bellows seals the space between the stationary sealing ring and the seal housing and also applies an axial load to the stationary seal ring which seal ring is biased axially into sealing engagement with the rotatable seal ring. Secondary seals also are provided between the bellows flange and the stationary seal ring and the bellows adapter and the seal housing.
For example, one bellows arrangement is disclosed in U.S. Pat. No. 5,901,965 wherein an O-ring defines a secondary seal between a non-rotatable or stationary seal ring and its holder. The O-ring only abuts against an outer axial surface of the seal ring. Thus, to transmit the axial load of the bellows to the stationary seal ring, the holder thereof includes a front surface which abuts against an opposing back surface of the seal ring. As a result, frictional contact between the opposed surfaces may result in undesirable seal face distortions.
In another bellows seal disclosed in U.S. Pat. No. 4,365,816, a flexible seal member with an L-shaped cross section is provided between a seal ring cup and a seal ring supported therein.
Also in spring type seals, U.S. Pat. No. 5,813,674 defines a non-bellows seal arrangement wherein a secondary seal between a seal ring and a seal ring holder is a gasket which has a C-shaped cross section and a spring disposed within the gasket. Another seal arrangement having a spring energized plastic seal is disclosed in U.S. Pat. No. 6,116,610. However, these spring energized secondary seals can slide axially and thus, do not support the axial loads between the spring and the seal ring.
An object of the invention is to provide a mechanical seal having an improved secondary seal arrangement which overcomes disadvantages associated with known mechanical seals.
In accord therewith, the invention relates to a mechanical seal having a spring loaded secondary seal which resiliently permits relative radial movement between a seal ring and a support element therefor, such as a bellows flange, and also supports axial loads between the seal ring and the support element.
In particular, a bellows type mechanical seal is provided wherein a non-rotatable, i.e. stationary, seal ring is axially movable and is axially loaded by a bellows which connects the stationary seal ring to the seal housing. The bellows includes a bellows flange at one end thereof which defines a support element that seats the stationary seal ring therein and has a secondary seal gasket therebetween. The opposite end of the bellows includes an annular adapter which seats within the seal housing and also has a secondary seal gasket therebetween. A further secondary seal gasket is provided between the rotatable seal ring and a support element therefor, namely a shaft sleeve.
The improved secondary seal gasket of the invention is provided in this mechanical seal preferably between the stationary seal ring and bellows flange and the rotating ring and the shaft sleeve, although the secondary seal of the invention also is usable for the bellows adapter.
The secondary seal gasket is an annular gasket having a C-shaped cross sectional shape defined by upper and lower legs and an end wall. The upper and lower legs and the end wall define a gasket jacket in which an annular spring is received. The annular spring is disposed between the legs to press the legs radially away from each other into sealing engagement with opposed surfaces of the bellows flange and a gasket shoulder defined on the seal ring. The upper and lower gasket legs therefore can move radially relative to each other to accommodate relative radial motion between the seal ring and the support element, thus reducing seal face distortion due to vibrations, differential thermal expansion or contraction, and differential pressure expansion or contraction. Further, spring and pressure forces act on and through the gasket jacket to effectively center the seal ring.
Additionally, the lower gasket leg is confined axially between an end wall of the gasket shoulder and an opposing face of the bellows flange such that the axial loads applied on the bellows flange by the bellows are transmitted axially to the seal ring through the lower gasket leg. While the lower leg is resilient, the lower leg is constrained axially and therefore is stiff in that direction, particularly since a hydraulic pressure force between the gasket legs stabilizes the lower leg and prevents buckling under axial loads.
The secondary seal arrangement and its application in a bellows type mechanical seal provides an improved seal having substantial axial load support while allowing radial motion of the parts which minimizes distortion of the faces and improves seal performance. Additionally, the radial position of the gasket shoulder relative to the mean bellows diameter serves to minimize the magnitude of the axial loads acting on the lower gasket leg even under full pressurization of the sealing chamber.